Systems and methods for liquid dynamic pressure testing

ABSTRACT

Certain implementations of the disclosed technology may include systems and methods for dynamic pressure testing of transducers in communication with a liquid. A method is provided that can include dynamically pressurizing a liquid in a cavity associated with a housing. While dynamically pressurizing the liquid, the method includes simultaneously measuring: a change in volume of the liquid; a test frequency response, by a test transducer in communication with the liquid; and a reference frequency response, by a reference transducer in communication with the liquid. The method may further determine a normalized frequency response of the test transducer, based at least in part on the test frequency response and the reference frequency response. The method may further provide an indication of the normalized frequency response of the test transducer and an indication of the bulk modulus of the liquid.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/801,002, filed 16 Jul. 2015, and published as U.S. Patent PublicationUS 2017/0016793 on 19 Jan. 2017, the contents of which are incorporatedherein by reference as if presented in full.

BACKGROUND

Pressure transducer assemblies that are used for measuring liquidpressures in certain systems can be adversely impacted by pressureripples and/or pressure pulses that propagate through the liquid.Pumping equipment, for example, may create pressure ripples in theliquid, and such ripples can negatively influence the accuracy of thepressure measured by the transducer, shorten the life expectancy of thetransducer, and/or destroy the transducer if it is not properlyprotected.

In certain systems, pressure ripple may be unavoidable, but it may bedesired to measure the steady-state pressure of a liquid whileminimizing the effects of pressure ripples. In such systems, a filterassembly may be inserted at the front end of the transducer to attenuateor eliminate the higher frequency ripples. However, the design of thefilter and the associated transducer must typically be matched to thespecific application and the individual system parameters.

In order to study the dynamic response of pressure transducers andpressure measurement systems in liquid media, a liquid-based dynamicpressure calibration apparatus is needed.

SUMMARY

Some or all of the above needs may be addressed by certainimplementations of the disclosed technology. The disclosed technologyincludes systems and methods for dynamic pressure testing of transducersin communication with a liquid or fluid, such as oil. In accordance withan example implementation of the disclosed technology, a method isprovided that can include dynamically pressurizing a liquid in a cavityassociated with a housing. While dynamically pressurizing the liquid,the method may include simultaneously measuring: a change in volume ofthe liquid; a test frequency response, by a test transducer incommunication with the liquid; and a reference frequency response, by areference transducer in communication with the liquid. The method mayfurther determine a normalized frequency response of the testtransducer, based at least in part on the test frequency response andthe reference frequency response. The method may further includeoutputting an indication of the normalized frequency response of thetest transducer. In certain example implementations, the method mayfurther include determining a bulk modulus of the liquid, and outputtingan indication of the bulk modulus of the liquid.

According to another example implementation, a test apparatus isprovided. The test apparatus may include: a housing including a cavityand configured for containing a liquid; a reference transducer mountedon the housing and configured for communication with the liquid; a testarticle including a test transducer, the test article configured formounting on the housing and further configured for communication withthe liquid; at least one computer processor in communication with thereference transducer and the test transducer; a piston in communicationwith the liquid and configured to slidingly engage with a portion of thecavity; and an actuator in communication with the piston and configuredto vibrate the piston to dynamically pressurize the liquid. The testapparatus is configured for simultaneously determining a bulk modulus ofthe liquid; and determining a normalized frequency response of the testarticle.

Other implementations, features, and aspects of the disclosed technologyare described in detail herein and are considered a part of the claimeddisclosed technology. Other implementations, features, and aspects canbe understood with reference to the following detailed description,accompanying drawings, and claims.

BRIEF DESCRIPTION OF THE FIGURES

Reference will now be made to the accompanying figures and flowdiagrams, which are not necessarily drawn to scale, and wherein:

FIG. 1 is a block diagram of an illustrative liquid-based dynamicpressure calibration apparatus 100 according to an exampleimplementation of the disclosed technology.

FIG. 2 is a block diagram of an illustrative test article 108, accordingto an example implementation of the disclosed technology.

FIG. 3 is a block diagram of another illustrative test article 108,according to an example implementation of the disclosed technology.

FIG. 4 is a block diagram of another illustrative test article 108,according to an example implementation of the disclosed technology.

FIG. 5 is a block diagram of another illustrative test article 108,including a mechanical filter 128, according to an exampleimplementation of the disclosed technology.

FIG. 6 is a block diagram of an example transducer assembly 600,including a filter comprising a small diameter tube 610, according to anexample implementation of the disclosed technology.

FIG. 7 shows experimental measurement results of the dynamic pressurecalibration apparatus 100, according to an example implementation of thedisclosed technology.

FIG. 8 shows experimental pressure and displacement of a liquid undertest.

FIG. 9a shows pressure vs. experimentally observed bulk modulus of aliquid under test.

FIG. 9b shows a model of effective bulk modulus of the liquid with 1%entrained air.

FIG. 10 is a flow diagram of a method according to an exampleimplementation of the disclosed technology.

DETAILED DESCRIPTION

Although preferred embodiments of the disclosed technology are explainedin detail, it is to be understood that other embodiments arecontemplated. Accordingly, it is not intended that the disclosedtechnology is limited in its scope to the details of construction andarrangement of components set forth in the following description orillustrated in the drawings. The disclosed technology is capable ofother embodiments and of being practiced or carried out in various ways.

As used in the specification and the appended claims, the singular forms“a,” “an,” and “the” include plural referents unless the context clearlydictates otherwise.

It is intended that each term presented herein contemplates its broadestmeaning as understood by those skilled in the art and may include alltechnical equivalents, which operate in a similar manner to accomplish asimilar purpose.

Ranges may be expressed herein as from “about” or “approximately” oneparticular value and/or to “about” or “approximately” another particularvalue. When such a range is expressed, another embodiment may includefrom the one particular value and/or to the other particular value.

By “comprising” or “containing” or “including” is meant that at leastthe named compound, element, particle, or method step is present in thecomposition or article or method, but does not exclude the presence ofother compounds, materials, particles, method steps, even if the othersuch compounds, material, particles, method steps have the same functionas what is named.

Referring now to the drawings, in which like numerals represent likeelements, exemplary embodiments of the disclosed technology are hereindescribed. It is to be understood that the figures and descriptions ofthe disclosed technology have been simplified to illustrate elementsthat are relevant for a clear understanding, while eliminating, forpurposes of clarity, other elements found in typical test assemblies.Those of ordinary skill in the art will recognize that other elementsmay be desirable and/or may be required in order to implement thedisclosed technology. However, because such elements are well known inthe art, and because they may not facilitate a better understanding, adiscussion of such elements is not provided herein.

FIG. 1 is a block diagram of an illustrative liquid-based dynamicpressure calibration test apparatus 100 according to an exampleimplementation of the disclosed technology. In certain exampleimplementations, the test apparatus 100 may perform two criticalmeasurements simultaneously: (1) frequency response of one or moretransducers in communication with the liquid, and (2) a bulk modulus ofthe liquid. These measurements may be utilized to characterize aresponse of a transducer, for example, as a function of pressure of theliquid, amount of air entrapped in the liquid, frequency of pressureripple in the liquid, and/or the presence (or absence) of pressureripple filtering structure(s) associated with the transducer.

According to an example implementation, the test apparatus 100 mayutilize a piston 112 to vibrate liquid 110 in communication with areference transducer 102 and a test transducer 104, for example, todynamically calibrate and/or experimentally determine the frequencyresponse of the test transducer 104. In an example implementation, thetest apparatus 100 may include a cavity in the form of a column having asame or similar diameter as the piston 112, for example, so that theliquid 110 is at least partially constrained to the shape of thecolumn-shaped cavity.

In accordance with certain example implementations of the disclosedtechnology, the test apparatus 100 may include one or more additionaltransducers or sensors 140, 142, 144. These additional sensors 140, 142,144 may be utilized, for example, to measure certain aspects associatedwith the test apparatus 100 and/or liquid 110 under test, including butnot limited to: vibrational characteristics, displacement of the variouscomponents, bulk modulus of the liquid 110, speed of pressure ripples inthe liquid 110, etc., as will be discussed further below.

In certain example implementations, the test transducer 104 may be partof a test article 108 for which the characterization is desired. Incertain example implementations, the test article 108 may include afilter section 106 having various geometries (as will be discussedbelow) and configured to dampen pressure ripples that may propagatethrough the liquid 110. According to certain example implementations,the test apparatus 100 may measure the bulk modulus of the liquid 110 atlow pressures. For example, the measurement of the bulk modulus of theliquid 110 may be achieved with the aid of additional sensors including,accelerometers, strain gauges, and/or additional dynamic pressuretransducers.

In accordance with an example implementation of the disclosedtechnology, the bulk modulus of the liquid 110 may provide an indicationof the amount of entrained and/or dissolved gases within the liquid 110.For example, gases such as air may be mixed or dissolved into the liquid110 and can add substantial damping to the dynamic response of a system.Therefore, knowledge of the bulk modulus may be critical for ameasurement and/or calibration of the frequency response of a systemwhen operating with liquid media.

In accordance with an example implementation of the disclosedtechnology, the test apparatus 100 may be utilized to measure a bulkmodulus of the liquid 110, for example, by a first method that mayinclude measuring a change in volume of the liquid 110 whilesimultaneously measuring the resulting change in pressure. According tocertain example implementations, the bulk modulus may be determined by asecond method that can include measuring the speed of sound within theliquid 110, for example, by using a difference in the time of arrival ofa wave between two dynamic pressure transducers mounted in differentlocations along the axis of the vibrating liquid 110.

In yet other disclosed implementations, the bulk modulus of the liquid110 may be measured by both of the above-mentioned methods for enhancedaccuracy and cross checking. In certain example implementations, thebulk modulus may be measured simultaneously (or separately) using bothof the above-mentioned methods. Certain example implementations mayinclude pressurizing the liquid 110 (and any entrained air) to anysuitable pressure range needed to characterize the associated testtransducer 104.

Certain example implementations of the disclosed technology may providefor measurement of the bulk modulus of the liquid 110, via theindependent methods described above (i.e., pressure vs. volume, speed ofsound), while simultaneously measuring the frequency (dynamic) responseof a test pressure transducer 104 and/or associated filter structure 106in communication with the liquid 110.

In certain example implementations of the disclosed technology, thereference transducer 102 may be utilized, for example, to provide areference measurement, for example, to account for various differentconfigurations associated with the test article 108. In certain exampleimplementations of the disclosed technology, the test apparatus 100 mayallow testing transducers 104 of various geometries and having variousassociated filters 106, tubes, etc., as will be discussed below withreference to FIGS. 2-6.

As discussed above, even a small amount of entrained or dissolved gas inthe liquid 110 may dramatically affect the system frequency responsemeasured by the test pressure transducer 104. Thus, in accordance withcertain example implementations of the disclosed technology, bysimultaneous measuring of the bulk modulus of the liquid 110 and thefrequency response of the transducer 104, accurate, reproduciblefrequency response calibration can be achieved.

According to an example implementation of the disclosed technology, andas depicted in FIG. 1, the test apparatus 100 can include housing with acavity to contain the liquid 110. In one example implementation, thehousing 118 may be machined into a suitable material. For example, inone implementation, the housing 118 may be formed in an acrylic block.In certain example implementations the housing 118 may be transparent toaid in visual confirmation of appropriate levels of fluid in the cavity,for example. As mentioned above, the main housing 118 cavity forcontaining the liquid 110 may be in the form of a column having a sameor similar diameter as the piston 112, for example, so that the liquid110 is at least partially constrained to the shape of the column-shapedcavity.

In an example implementation, the housing 118 associated with the testapparatus 100 may include two or more pressure transducer mounting portslocated directly across from each other. For example, in one embodiment,the pressure ports may be configured in a symmetric geometry withopenings or bores in communication with the main cavity and normal tothe axis 120 of the housing 118 and piston 112. Such a configuration mayprovide substantially equal pressure ripples via the liquid 110 to theopposing transducers.

In an example implementation, the piston 112 may include one or moreo-rings to act as a liquid seal, and a top portion of the piston 112with the o-rings may fit inside a bottom portion of the cavity, whilethe bottom portion of the piston 112 may be in communication with ordirectly attached to shaker table or similar actuator (not shown).

Once assembled, the test apparatus 100 may be filled with the workingliquid media 110 via an additional fill tube (not shown). In accordancewith an example implementation of the disclosed technology, the processof filling the cavity with the liquid may be critical to the accuracyand performance of the calibration and measurement. For example, and aspreviously discussed, air (or other gas) bubbles within the liquid 110may compress as the piston 112 vibrates, resulting in negligible (forexample, <1 kPa) dynamic pressures within the system, since air iseasily compressible, but liquid is typically not. However, without anyair within the system, the liquid 110 itself may only slightly compress,yielding a possible large magnitude of dynamic pressures (forexample >350 kPa). The general example of the dynamic pressures withinthe cavity, as discussed here, are for example only. Other factors, suchas the actuator/piston/shaker size and input power may influence thedynamic pressures (in addition to the amount of entrained air. Forexample, larger shakers and higher input power can be used to createlarger dynamic pressures over a variety of frequencies. In certainexample implementations, the test apparatus 100 may be configured toproduce large peak-to-peak dynamic pressures, for example, >350 kPa (50psi), over the frequency range of approximately 10 Hz to approximately 5kHz. In other example implementations, the frequency range may beextended to upwards of 20 KHz or greater.

In accordance with an example implementation of the disclosedtechnology, one or more of the transducers 102 104 associated with thetest apparatus 100 may be in communication with a multi-channelacquisition system 130. In certain example implementations, theacquisition system 130 may include one or more computer processors incommunication with a memory. In certain example implementations, theacquisition system 130 may include one or more of: signal conditioners,electronic filters, analog-to-digital converters, etc., for example, toreceive, condition, convert, and store signals received from the varioussensors associated with the test apparatus 100.

In an example implementation, the operation of the test apparatus 100may be validated with two equally configured dynamic pressuretransducers mounted directly across from each other at substantially thesame vertical location on the housing 118. The housing 118 cavity may befilled with the test liquid (such as oil, for example) and preloaded,for example, by securing the housing 118 to a stationary portion of theshaker/actuator. In accordance with an example implementation of thedisclosed technology, the preloading may improve the shape of theresulting pressure waveforms, for example, to correspond with the actualdynamic displacement of the shaker/actuator, which in certainembodiments may be sinusoidal. Furthermore, the measured pressureamplitude and/or phase may vary as a function of frequency of thevibration due to various resonances of the system. Thus, the operationof test apparatus 100 and the equally configured dynamic pressuretransducers may be further validated by comparing their measuredfrequency responses to verify that they are substantially equal. Incertain example implementations, the validation process described heremay be utilized prior to actual testing and characterization of a testarticle 108.

In certain example embodiments, the test apparatus 100 may include thetwo equally configured dynamic pressure transducers mounted directlyacross from each other (not shown) on the cavity housing 118 in additionto the reference transducer 102 and the test article 108 (also mounteddirectly across from each other). In this embodiment, the validation ofthe test may be performed at the same time as the test article 108characterization without requiring the separate validation process,which may involve draining and re-filling the cavity with the liquid110.

In accordance with an example implementation of the disclosedtechnology, air-free liquid filling of the cavity housing 118 may beachieved by placing the assembled test apparatus 100 in a vacuum chamberwith the fill tube (not shown) submerged in liquid. Upon evacuating thevacuum chamber, air may be slowly released from the liquid into thevacuum chamber resulting in air-free filling of the cavity housing 118with liquid. In certain example implementations, the fill tube may thenbe crimped and/or welded closed.

In certain implementations, for example, where the test apparatus 100housing 118 may include a transparent or translucent material (such asacrylic, for example), visual inspection of air bubbles within theliquid-filled cavity housing 118 may be enabled. If air bubbles areidentified, vacuum refilling may be redone.

In accordance with certain example implementations of the disclosedtechnology, and with reference to FIGS. 2-5, the test article 108 mayinclude a pressure transducer assembly that utilizes a filter assemblyadapted to attenuate certain pressure ripple frequencies, for example,to attenuate certain resonances or ranges of frequencies. In certainexample implementations, the filter assembly may comprise one or moremechanical structures and configurations, including but not limited to:

-   -   tubes 106 (see FIG. 2);    -   various shaped cavities 120 (see FIG. 3);    -   tubes 106 with various lengths 122 and diameters (see FIG. 3);    -   sensor 104 diaphragms with various diameters 124 (see FIG. 4);    -   porous structures 128 (see FIG. 5); and/or    -   combinations of the above structures and configurations.

In accordance with an example implementation of the disclosedtechnology, the test article 108 may be tuned by the filter assembly(and/or the associated various configurations) to achieve a desiredfrequency response and/or attenuation of certain frequencies. Thoseskilled in the art may appreciate that certain pressure media maycomprise high frequency pressure ripples that can interfere with theaccuracy of the sensing element and shorten its operable lifespan. Thepressure transducer assembly disclosed herein may be tuned via thefilter assembly to eliminate undesirable high frequency ripples and passthrough desirable static and quasi-static pressures. Specifically,dependent on the properties of the pressure media to be measured, suchas its viscosity, the filter assembly and sensor configurations may beadjusted to achieve desired dampening parameters.

With reference to FIG. 2, one skilled in the art may appreciate thatnarrowing the tube 106 (i.e., decreasing the diameter) may enhanceattenuation. However, if the tube 106 is too narrow for the appliedpressure media, desirable low frequency components (e.g., static andquasi-static pressures), which may interfere with the accuracy of thesensing element 104, may also be eliminated. Conversely, if the tube 106is too wide, high frequency ripples may not sufficiently eliminated,which may also interfere with the accuracy of the sensing element 104and decrease its operable lifespan.

With reference to FIG. 3, by varying only the length 122 of the tube 106and/or other associated components (such as the cavity volume 120,etc.), a single pressure transducer assembly design may be tuned to manydifferent systems having varying pressure media properties. In certainexample implementations, the actual length 122 of the tube 106 may bechanged. For example, to shorten the filter assembly, the tube 106 maybe pushed towards the test sensor 104, which consequently mayeffectively reduce the area of the cavity volume 120 around the sensingelement 104. In certain example implementations, shortening the tube 106may expose the pressure media (i.e., liquid 110) to more of the sensorchannel defined within the cavity housing 118, and may have minimalinfluence on the overall frequency response. Conversely, to lengthen thetube 106, it may be pulled away from the test sensor 104, whichconsequently may effectively increase the area of the cavity volume 120around the sensing element 104.

In accordance with an example implementation of the disclosedtechnology, certain test filter assemblies may be configured so the tube106 may slide within the pressure transducer assembly to vary the filterproperties. Once the desired tuning is achieved, the filter assembly maybe fixed, for example, standard welding techniques.

In accordance with another example implementation of the disclosedtechnology, certain test filter assemblies may be configured with customlengths and/or diameters of the tube 106 for specific filteringproperties. Thus, pressure transducer assemblies having commonproperties may be manufactured, and each assembly can be subsequentlytuned to a desired system, thereby reducing costs associated withdesigning one unique pressure transducer assembly for one unique system.

FIG. 6 depicts an example transducer assembly 600, according to anexample implementation of the disclosed technology. In this exampleassembly 600, a sensing element 602 may be in communication with acavity 604 defined by a cap 606, which may be filled with a liquid via amedia entrance 608 and the small diameter tube 610. For example, theliquid may enter the media entrance 608 and travel through the tube 610to the cavity 604. In an example implementation, the pressures exertedby the liquid at the media entrance 608 may be filtered by the tube 610and in communication with the sensing element 602.

As previously described and with continued reference to FIG. 1, the testapparatus 100 may include additional sensors 140, 142, 144, etc.,through which bulk modulus may be measured using one or more measurementtechniques. For example, one measurement technique may utilize twoaccelerometers: one mounted to the shaker arm and a second on the top ofthe housing 118. In an example implementation, a strain gauge may bemounted on the piston 112. The acceleration of the shaker arm may beintegrated twice to determine the displacement of the shaker arm.Similarly, the displacement of the cavity housing 118 may be determinedfrom its measured (and twice integrated) acceleration. The deflection ofthe piston cavity housing 118 may be determined from the strain gaugemeasurement. In an example implementation, the measured deflection fromthese three sensors may be combined/analyzed to determine the deflectionof the liquid 110 column in the cavity. With the known initial volume,the bulk modulus of the liquid can be computed using the followingequation:

$\begin{matrix}{E = {V \cdot \left( \frac{\partial p}{\partial V} \right)}} & (1)\end{matrix}$

where V is the initial volume of the liquid and

$\frac{\partial p}{\partial V}$is the change in pressure over change in volume. When practically used,most fluids have some quantity of dissolved and entrained air whichgives rise to an effective bulk modulus of a liquid-air mixture, Eeff,which can be predicted using the following equation:

$\begin{matrix}{{Eeff} = \frac{E_{Oil}}{1 + {{\alpha\left( \left( \frac{p_{o}}{p} \right)^{\frac{1}{K}} \right)} \cdot \left( {\frac{E_{Oil}}{K \cdot p} - 1} \right)}}} & (2)\end{matrix}$

where α is the percent volumetric content of entrained air at theinitial pressure, p₀ is the initial pressure, p is the applied pressure,K is the polytropic constant of air and E_(Oil) is the bulk modulus ofthe liquid (for example, oil) under test.

As discussed previously, the strain gauge mounted on the piston 112, theaccelerometer on the shaker arm, and an additional accelerometer to thetop of the cavity housing may 118 enable the deflection (i.e.,compression) of the liquid/air media to be measured, albeit indirectly.

FIG. 7 shows measurement plots (from top to bottom) of applied pressure,measured strain/deflection, acceleration/displacement of the housing 118(which in this case is made from an acrylic block), and theacceleration/displacement of the shaker arm, each as a function of timeon the x-axis. The bottom two acceleration plots (continuous lines) areintegrated twice to determine the associated displacement (dashed lines)of the cavity housing and shaker arm. As anticipated, the shaker armexhibits the greatest measured displacement. In accordance with anexample implementation, the deflection of the liquid column in cavityhousing 118 may be determined by taking a difference of the displacementof the cavity housing 118 and the displacement of the shaker arm.Furthermore, in an example implementation, the deflection of the piston112 may be added to the above difference as it is compressing theliquid, resulting in a determined deflection of the liquid column withthe change in pressure.

FIG. 8 shows the experimental pressures experienced by the referencetransducer 102 and a test article 108 (top plot), and calculateddisplacement of the liquid 110 (bottom plot). In an exampleimplementation, and from the measurement of displacement of the liquid110, the change in volume may be computed as a percentage of the totalvolume within the liquid filled column.

FIG. 9a shows pressure vs. experimentally observed bulk modulus of aliquid under test, and FIG. 9b shows a Wylie model of effective bulkmodulus of the liquid with 1% entrained air. These plots show anexperimentally observed effective bulk modulus of 0.03 GPa which is inagreement with the predicted bulk modulus for the liquid used in anexample test with 1% entrained air at these pressures. Note that theseplots indicate that the data exhibits a significant hysteresis, whichmay be related to the low test pressures. As the Wylie model in FIG. 9bpredicts, the bulk modulus approaches its true value at substantiallyhigher pressures ˜10 MPa (1500 psi) with smaller error predicted athigher pressures. In accordance with an example implementation of thedisclosed technology, and based upon the measured effective bulkmodulus, it may be determined that the specific example liquid in thisexperimental system example contains approximately 1% air.

In accordance with an example implementation of the disclosedtechnology, the effective bulk modulus of a liquid may primarily dependon pressure and entrained air, which has been confirmed by previousexperimenters. However, certain embodiments of the disclosed technologyprovide significant technical improvements over previous or conventionalmeasurement methods in that the bulk modulus is experimentally observedto estimate entrained air, while simultaneously capturing the frequencyresponse of a given geometry of a test article 108. In an exampleimplementation, the correlation of entrained air in the liquid 110 andthe observed damping over the frequency response enables a prediction ofthe performance of a pressure sensor (configured with a similar or samegeometry as the test article 108) within a different system of the sameworking liquid.

In accordance with an example implementation of the disclosedtechnology, the bulk modulus of the liquid under test can also bedetermined based upon the speed of sound in the liquid media. Forexample, the speed of sound depends on the bulk modulus of the fluidthrough the following equation:

$\begin{matrix}{c = \sqrt{\frac{K}{p}}} & (3)\end{matrix}$

where c is the speed of sound, K is bulk modulus and p is the density ofthe fluid. Using the known distance along the vibrating column of liquid110, for example, between a first and second dynamic pressure transducer(not shown), and a measured difference in the wave time of arrival ateach of these transducers, the speed of sound in the liquid 110 may beextracted. According to an example implementation of the disclosedtechnology, with two independent measurements of bulk modulus, a greaterlevel of measurement confidence may be achieved.

FIG. 10 is a flow diagram of a method 1000 according to an exampleimplementation of the disclosed technology. In block 1002, the method1000 includes dynamically pressurizing a liquid in a cavity associatedwith a housing. While dynamically pressurizing the liquid, and asindicated in block 1004, the method 1000 includes simultaneouslymeasuring: a change in volume of the liquid; a test frequency response,by a test transducer in communication with the liquid; and a referencefrequency response, by a reference transducer in communication with theliquid. In block 1006, the method 1000 includes determining a normalizedfrequency response of the test transducer, based at least in part on thetest frequency response and the reference frequency response. In block1008, the method 1000 includes outputting an indication of thenormalized frequency response of the test transducer.

In certain example implementations, the simultaneously measuring canfurther include one or more of: measuring, by one or more of thereference transducer and the test transducer, a pressure of the liquidin the housing; measuring a displacement of a piston structure incommunication with the liquid; determining a change in volume of theliquid based on the displacement of the piston; determining a bulkmodulus of the liquid based on the measured pressure and the determinedchange in volume of the liquid; and outputting an indication of the bulkmodulus of the liquid.

In certain example implementations, the determination of the bulkmodulus of the liquid may be based on the measured speed of sound in thepressurized liquid.

Certain example implementations can include filtering, by a mechanicalfilter, the pressurized liquid in communication with the testtransducer. In accordance with certain example implementations of thedisclosed technology, the mechanical filer may include one or more of: aporous structure; a narrow tube; a cavity; a recessed structure; and/ora surface area of a test diaphragm associated with the test transducerthat differs from a surface area of a reference diaphragm associatedwith the reference transducer.

In certain example implementations, determining the normalized frequencyresponse can include storing in a memory in communication with one ormore computer processors, the test frequency response and the referencefrequency response, and comparing, by the one or more computerprocessors, the test frequency response and the reference frequencyresponse.

In one example implementation, the test and reference transducersinclude different structures. In another example implementation, thetest and reference transducers comprise substantially similarstructures.

According to an example implementation of the disclosed technology, thetest transducer and the reference transducers are disposed at an equalvertical position in the housing and in communication with the liquidunder test. In certain example implementations, the test transducer andthe reference transducers may be disposed opposing one another in thehousing.

According to another example implementation, a test apparatus isprovided. The test apparatus may include: a housing comprising a cavityand configured for containing a liquid; a reference transducer mountedon the housing and configured for communication with the liquid; a testarticle comprising a test transducer, the test article configured formounting on the housing and further configured for communication withthe liquid; at least one computer processor in communication with thereference transducer and the test transducer; a piston in communicationwith the liquid and configured to slidingly engage with a portion of thecavity; and an actuator in communication with the piston and configuredto vibrate the piston to dynamically pressurize the liquid. The testapparatus is configured for simultaneously determining a bulk modulus ofthe liquid and determining a normalized frequency response of the testarticle.

In certain example implementations, determining the normalized frequencyresponse can include storing, in a memory in communication with the oneor more computer processors, a test frequency response of the testtransducer, and a reference frequency response of the referencetransducer. In certain example implementations, determining thenormalized frequency response can include comparing, by the one or morecomputer processors, the test frequency response and the referencefrequency response.

In an example implementation, determining the bulk modulus may includeone or more of: dynamically pressurizing, by the piston, the liquid inthe cavity; measuring, by one or more of the reference transducer andthe test transducer, a pressure of the liquid; measuring a displacementof the piston in communication with the liquid; determining a change involume of the liquid based on the displacement of the piston; anddetermining the bulk modulus of the liquid based on the measuredpressure and the determined change in volume of the liquid.

In accordance with an example implementation of the disclosedtechnology, the test apparatus may further include a first transducerdisposed at a first distance from the piston and configured to provide afirst measurement signal; and a second transducer disposed at a seconddistance from the piston and configured to provide a second measurementsignal. In certain example implementations, determining the bulk moduluscan include measuring a speed of sound in the liquid. For example, thespeed of sound in the liquid may be based on a time difference of thefirst and second measurement signals.

In accordance with certain example implementations of the disclosedtechnology, the test article may include a filter including or more of aporous structure, a narrow tube, a cavity, a recessed structure, and/ora surface area of the test diaphragm associated with the test articlethat differs from a surface area of a reference diaphragm associatedwith the reference transducer.

In certain example implementations, at least one computer processor maybe configured to compute a normalized frequency response of the testarticle based on a comparison of a test frequency response of the testtransducer and a reference frequency response of the test article.

In one example implementation, the test and reference transducerscomprise different structures. In another example implementation, thetest and reference transducers comprise substantially similarstructures. In certain example implementations, the test article and thereference transducer are disposed opposing one another. In certainexample implementations, the test article and the reference transducerare equidistant from the piston.

Certain example implementations of the test apparatus 100 may measurethe frequency response of a transducer and associated geometry, whilesimultaneously determining the bulk modulus of the fluid through twoseparate techniques. From bulk modulus, the entrained and/or dissolvedair can be estimated, providing a critical advancement in the field ofdynamic pressure calibration.

Numerous characteristics and advantages have been set forth in theforegoing description, together with details of structure and function.While the disclosed technology has been presented in several formsherein, it may be apparent to those skilled in the art that manymodifications, additions, and deletions, especially in matters of shape,size, and arrangement of parts, can be made therein without departingfrom the spirit and scope of the disclosure and its equivalents as setforth in the following claims. Therefore, other modifications orembodiments as may be suggested by the teachings herein are particularlyreserved as they fall within the breadth and scope of the claims.

The invention claimed is:
 1. A computer-implemented method, comprising: dynamically pressurizing a liquid in a cavity associated with a housing; while dynamically pressurizing the liquid, simultaneously measuring: a test frequency response, by a test transducer in communication with the liquid, wherein the test transducer includes a filter section configured to dampen pressure ripples; a reference frequency response, by a reference transducer in communication with the liquid; determining, by one or more computer processors, a normalized frequency response of the test transducer, based at least in part on the test frequency response and the reference frequency response; and outputting an indication of the normalized frequency response of the test transducer.
 2. The method of claim 1, wherein the filter section is configured to attenuate pressure ripples over a range of pressure ripple frequencies.
 3. The method of claim 1, wherein the filter section is configured to dampen high frequency pressure ripples.
 4. A test apparatus, comprising: a housing comprising a cavity configured for containing a liquid; a reference transducer mounted on the housing and configured for communication with the liquid; a test article comprising a test transducer and a filter configured to dampen pressure ripples, the test article coupled to the housing and further configured for communication with the liquid; at least one acquisition system in communication with the reference transducer and the test transducer; a piston in communication with the liquid and configured to slidingly engage with a portion of the cavity; wherein the acquisition system is configured to determine a normalized frequency response of the test article.
 5. The test apparatus of claim 4, wherein the filter is configured to attenuate pressure ripples over a a range of pressure ripple frequencies.
 6. The test apparatus of claim 4, wherein the filter is configured to dampen high frequency pressure ripples.
 7. The test apparatus of claim 4, wherein the acquisition system is further configured to determine a bulk modulus of the liquid.
 8. The test apparatus of claim 7, wherein: the piston is configured to dynamically pressurize the liquid in the cavity; one or more of the reference transducer and the test transducer are configured to measure a pressure of the liquid; a displacement of the piston is configured to measure a change in the volume of the liquid; and the acquisition system is further configured to determine the bulk modulus based on the measured pressure and the determined change in volume of the liquid.
 9. The test apparatus of claim 4, wherein the acquisition system is further configured to determine the normalized frequency response by: storing, in a memory in communication with the acquisition system: a test frequency response of the test transducer; and a reference frequency response of the reference transducer; and dividing the test frequency response by the reference frequency response.
 10. The test apparatus of claim 4, wherein the filter comprises one or more of: a porous structure; a narrow tube; a cavity; and a diameter of the test diaphragm associated with the test article that differs from a diameter of a reference diaphragm associated with the reference transducer.
 11. The test apparatus of claim 4, wherein the acquisition system is configured to compute a normalized frequency response of the test article based on dividing a test frequency response of the test transducer by a reference frequency response of the test article. 